Messenger No.
37 (September 1984)

ADS BibCode:1984Msngr..37....1RAuthor(s)/Affiliation(s):Raffi, G.; Tarenghi, M.AA(ESO) AB(ESO)Abstract:With the expenditure of missions from Europe to Chile showing a steady increase, not only because of flight prices but also because of the rise in infrastructure upkeep of remote sites, along with a clear tendency to lower the cost of satellite transmission, it seems to us that remote control will become an economical system to operate telescopes.

ADS BibCode:1984Msngr..37....7DAuthor(s)/Affiliation(s):Dekker, H.; D'Odorico, S.AA(ESO) AB(ESO)Abstract:EFOSC, the ESO Faint Object Spectroscopic Camera, will be available to users as of April 1, 1985 at the Cassegrain focus of the 3.6 m telescope. The instrument was mounted for the first time at the telescope in June 1984 for a short test period. The optical components were not yet fully optimized, and only part of the grisms and filters were available. It was, however, possible to test successfully the instrument functions and to carry out a few observations in direct imaging and spectroscopic modes. The results prove the high efficiency and the versatility of the instrument. A full description of EFOSC will be given in a next issue of the Messenger.References:Condon, J. J., Hicks, P. D., and Jauncey, D. L.: 1977, Astron. J. 82, 692.MacAlpine, G. M., and Williams, G.A., 1981, Astrophys. J. Suppl.45,113.

ADS BibCode:1984Msngr..37....8CAuthor(s)/Affiliation(s):Courvoisier, T. J.-L.AA(Space Telescape European Coordinating Facility)Abstract:In order to understand the overall spectra of active galactic nuclei (AGN), the structure of the emission regions was studied. A wind and shock model, developed to explain this structure, is aimed at understanding individual objects such as the quasar QSO 3C 273. The European X-ray satellite EXOSAT, which includes a low energy imaging telescope and a medium energy experiment was used to observe the spectrum of 3C 273 at several wavelengths. The components of the spectrum include the 1R-optical synchroton emission, the thermal component in the optical spectrum, and the comptonized X-ray spectrum.References:(1) M. Camenzind and T. J.-L. Courvoisier: 1983, Ap. J. 266, L83.(2) B. G. Taylor, R. D. Andresen, A. Peacock and R. Zobl: 1981, SpaceScience Reviews 30, 479.(3) M. Turner et al., in preparation.

ADS BibCode:1984Msngr..37...10FAuthor(s)/Affiliation(s):Furenlid, I.; Meylan, T.AA(Department of Physics and Astronomy, Georgia State University, Atlanta) AB(Department of Physics and Astronomy, Georgia State University, Atlanta)Abstract:The closest known star apart fram the Sun is a very faint object called Praxima Gentauri. The nextclosest star is Alpha Centauri or Rigil Kentaurus which forms a binary system having components designated as a Gen A and a Gen B. The component called a Gen A is of particular interest because it strongly resembles the Sun. As a matter of fact, it resembles the Sun to such an extent that it has been called a solar twin. Several researchers have taken a close look at a Gen A using different means in trying to find out exactly what its praperties are. Photometry of an object as bright as a Gen A with acooler component within 18 arcsec of angular distance may suffer fram systematic errors. And analysing spectra of a Gen A is hard to do with sufficient accuracy.

ADS BibCode:1984Msngr..37...11HAuthor(s)/Affiliation(s):Heske, A.; Wendker, H. J.AA(Hamburger Sternwarte, Hamburg, FRG) AB(Hamburger Sternwarte, Hamburg, FRG)Abstract:OB associations are usually thought to be the youngest stars in aspace volume infected by the virus of star formation. The combined effects of strang UV radiation and stellar winds quickly disperse the parent interstellar cloud and thus end the star formation episode. Details of this picture are, however, subject to debate, especially such questions as when, where and how long which types of stars are formed within the parent cloud. Only a vast amount of observations on as many associations and young open clusters as possible will allow us to draw final conclusions.

ADS BibCode:1984Msngr..37...13VAuthor(s)/Affiliation(s):Vidal, S.AA(ESO)Abstract:The main job of the computer operator is organizing and saving the data acquired with all telescopes operating at La Silla in a magnetic tape bank. A short description of his duties and of the standardized procedures is given here intending to make them widely known.References:(1) Imbert, M., and Prevot, L., 1981, The Messenger25, 6.(2) Wells, D.C., and Greisen, E.W., 1979, in Image Processing inAstronomy, Ed. G. Sedmak, M. Capaccioli, R. S. Allen, OsservatorioAstronomico di Trieste.

ADS BibCode:1984Msngr..37...14RAuthor(s)/Affiliation(s):Reipurth, B.AA(Universitetets Astronomiske Observatorium, Copenhagen, Denmark)Abstract:The Horsehead, a new-born Bok globule which is actively forming stars, is described. It appears likely that this activity was triggered by the same processes which are presently excavating it from its parental cloud. A second Bok globule, NGC 5367, which comprises a cluster of nebulous stars embedded in the cometary globule CG 12, is also discussed. The combined effects of forces such as ultraviolet radiation and erosion will probably lead to the destruction of its original globule. Optical and infrared photometry, IDS spectra, and CCD images were used to study the stars in these two globules.

ADS BibCode:1984Msngr..37...19MAuthor(s)/Affiliation(s):Materne, J.AA(Berlin, Technische Universitaet, Berlin, West Germany)Abstract:The possible detection of a rotating galaxy cluster is reported. The cluster was observed with the Ariel satellite in the southern hemisphere (03 h, 16 m, -44 degrees) and is tentatively named SC 0316-44. On the basis of measurements of the velocity dispersion of the individual galaxies it could not be shown that the observations were not simply the result of two clusters partially overlapping.

ADS BibCode:1984Msngr..37...21JAuthor(s)/Affiliation(s):Joubert, M.; Kunth, D.AA(CNRS, Laboratoire d'Astronomie Spatiale, Marseille, France), AB(CNRS, Institut d'Astrophysique, Paris, France)Abstract:The observational results for a sample of Wolf-Rayet (WR) stars in lazy galaxies are discussed within the context of a general deep search of WR emission in relatively distant objects conducted with the Palomar 200-inch, Las Campanas 2.5-m, and the La Silla 1.5- and 3.6-m telescopes. The sample is composed of observations in the range between 4600 and 4700 A. WR stars were positively detected in three galaxies and are suspected in 16 others at 1.0 sigma over the underlying background. It is found that for the three best observed cases of WR emission, the equivalent width of the emission line was in no way similar to that of the H-beta emission line. The spread in EW (H-beta) emission by a factor of 20 corresponded to a nearly constant WR equivalent width of about 8 A, but not at all to the number of ionizing massive stars. It is suggested that WR stars in lazy galaxies occur in a population of stars less massive than 60 solar mass and that they are linked to the early evolutionary phase of the burst of star formation. A tracing of a typical broadband WR emission in the spectrum of Mkn 750 is provided.

ADS BibCode:1984Msngr..37...24DAuthor(s)/Affiliation(s):Dodorico, S.; Ponz, D.AA(EUROPEAN Southern Observatory, Garching, West Germany), AB(EUROPEAN Southern Observatory, Garching, West Germany)Abstract:Results of an analysis of the spectral data reduced by the CASPEC instrument are reported. In the wavelength calibration performed by CASPEC calibration lines are identified according to a detection criterion which is based on line-width and the intensity above the background. In the commissioning phase nine spectra of 4 velocity standard stars are reduced using the standard procedure in the Munich Image Data Analysis System (MIDAS) of the ESO. The procedures followed by CASPEC for reducing a flat-field CCD image is described. As an example, two extracted orders from a 25 min. exposure of the 12.1 visual magnitude star LTT 3864 are presented.References:(1) S. D'Odorico, C. la Dous, D. Ponz and J. F. Tanne, "An Atlas of theThorium-Argon Spectrum for the ESO Echelle Spectrograph",ESO Scientific Report No. 2.(2) The Astronomical Almanac, 1984, Naval Observatory and RoyalGreenwich Observatory.(3) MIDAS, Munich Image Data Analysis System, 1984, ESO OperatingManual No. 1.

ADS BibCode:1984Msngr..37...30YAuthor(s)/Affiliation(s):Yorke, H. W.AA(Universitäts-Sternwarte, Göttingen, F. R. G.)Abstract:Some of the most spectacular astronomical photographs and favourite subjects for popular astronomical slide shows are colour pictures of H 11 regions. Probably every astronomer, both amateur and professional, is familiar with the nebula in Orion, M 42. Shaped like an opened fan, this well-known H I1 region ("H II" is the technical term for ionized hydrogen) appears to be yellow in its bright core and fades out to red and then a faint bluish hue towards the outer perimeter. Of course, the exact colours and size of the Orion Nebula, M 42, is dependent on the type of colour film used and the amount of light gathered. Longer exposure times tend to make the nebula appear larger, expanding outward in the direction of the fan's perimeter. Short exposures of the nebula (or using the eye instead of film) reveal the presence of four bright stars in its core, the "Trapezium", so named because of their relative geometrical positions. These stars cannot be seen on longexposure pictures, because the light from the nebular core saturates the film.References:(1) Strömgren, B.: 1939, Astrophys. J. 89, 526.(2) Spitzer, L.: 1949, Astrophys. J. 107, 6.(3) Tenorio-Tagle, G.: 1979, Astron. Astrophys. 71,59.(4) Yorke, H. W., Tenorio-Tagle, G., Bodenheimer, P.: 1984, Astron.Astrophys. 243 (in press).(5) Lynds, B.T., O'Neil, E.J.: 1982, Astrophys. J. 263, 130.(6) Lada, C. J., Gull, T. R., Gottlieb, C.A., Gottlieb, E. W.: 1976, Astrophys.J. 203, 159.

ADS BibCode:1984Msngr..37...35LAuthor(s)/Affiliation(s):Lundstrom, I.; Stenholm, B.AA(Lund Observatory, Sweden) AB(Lund Observatory, Sweden)Abstract:Ouring the last decades we have seen the advent of new technology detectors, which no longer contain a photographic emulsion as a last step. These detectors, such as the lOS (Image Oissector Scanner) for spectroscopic work and the CCO (Charge-Coupled Oevice) for field imaging, produce digitized data, which can easily be stored on a disk or on a magnetic tape. In this short article we will report some of our experiences of the lOS devices of ESO. The lOS at the 3.6 m telescope was taken into use in 1978 and the one at the 1.52 m telescope followed two years later. Although we have had the opportunity to use both instruments we will concentrate on a programme performed exclusively with the 1.52 m telescope.References:Lundström, I. and Stenholm, B.: 1984, Astron. Astrophys. (in press).Jones, D. H. P., Evans, D. S. and Catchpole, R. M.: 1969, Observatory89,18.Sanduleak, N.: 1976, Publ. Warner & Swasey Obs. 2,3.Smith, L. F. and Aller, L. H.: 1971, Astrophys. J. 164, 275.Stephenson, C. B. and Sanduleak, N.: 1977, Astrophys. J. Suppt. 33,459.Webster, B. L.: 1969, Monthty Not. Roy. Astron. Soc. 143, 79.

ADS BibCode:1984Msngr..37...36SAuthor(s)/Affiliation(s):Sadler, E.AA(ESO)Abstract:The use of charge-coupled device (CCD) cameras in galaxy photometry offers a number of significant advantages over traditional photoelectric and photographic techniques. CCOs have a high quantum efficiency compared to photographic plates, and their response is linear over a large range of brightness. Since they are two-dimensional detectors, the centring problems of photoelectric photometers are avoided, and object and sky can be observed simultaneously. Of course, there are also some disadvantages; the CCD is much smaller in area than a photographie plate, and the read-out noise is a limiting factor for short exposures. However, one area in which CCD detectors are particularly valuable is in studying the inner regions of nearby galaxies, and in particular the colours and colour gradients in galactic nuclei. Here, the smaller size of the CCD is no disadvantage as we are studying objects 1-2 are minutes in angular size. Since the luminosity profile of a galaxy rises sharply towards the centre, saturation effects and the non-linear response of the emulsion present problems for photographie work, while it is extremely hard to obtain photoelectric aperture photometry with diaphragms smaller than 10-15" because of the difficulty in centring the galaxy accurately. The resolution of the GGO image, on the other hand, is limited only by the pixel size (0"47 at the Danish 1.5 m telescope) and the seeing (usually 1-2" at La Silla). This allows us a fascinating glimpse into the innermost regions of many nearby galaxies, and may provide new insight into the mechanisms responsible for "active" nuclei in galaxies.